CN104977024A - Solar blind ultraviolet remote sensing camera absolute radiometric calibration coefficient in-orbit correction method - Google Patents

Abstract

The present invention relates to a solar blind ultraviolet camera absolute radiometric calibration equation coefficient in-orbit correction method, wherein a camera is subjected to laboratory absolute radiometric calibration to obtain the absolute radiometric calibration coefficient and the non-uniformity correction coefficient of the camera, the atmosphere background radiation value calculated based on the atmosphere radiation transmission model can be considered as the true background radiance when the camera in-orbit operating meets a certain constraint of the imaging mode, the location and the illumination condition, the background radiance is inverted according to the laboratory absolute radiometric calibration coefficient and the image local gray mean, and a linear regression method is used to analyze the inverted radiance value and the true radiance value so as to achieve the in-orbit correction of the calibration equation coefficient. According to the present invention, according to the solar blind ultraviolet spectrum atmosphere background radiation characteristic, the high-frequency and operational in-orbit absolute radiometric calibration of the solar blind ultraviolet spectrum remote sensor can be supported, and the blank of the in-orbit absolute radiometric calibration method of the domestic camera at the spectrum is filled.

Description

A kind of day blind ultraviolet remote sensing camera Absolute Radiometric Calibration Coefficients modification method in-orbit

Technical field

The present invention relates to a kind of day blind ultraviolet remote sensing camera Absolute Radiometric Calibration Coefficients modification method in-orbit, belong to aerospace optical remote sensing technical field.

Background technology

From 20 century 70s, the U.S. successively reflects the OGO-4 (1976) for the detection of ultraviolet spectral coverage atmospheric remote sensing, S3-4 (1978), DE-1 (1981), VIKING (1986), Polar BEAR (1986), AURA (2004), these ultraviolet detectors mostly adopt measurement ultraviolet fixed star to carry out absolute radiometric calibration in-orbit, as " Calibration of the Viking Auroral Imager Using Ultraviolet Stars ", mention in literary compositions such as " SatelliteObservations with the VUPI Instrument " and adopt single-point absolute radiometric calibration method, there is two problems in this calibrating method: first, by the scale-up factor responded fixed star point target imaging determination camera and between stellar radiation flux density, make to carry out radiation calibration hypothesis camera resonse characteristic in this way and meet proportionate relationship y=kx, namely think that camera absolute radiometric calibration equation migration amount is 0, larger radiation calibration error can be brought when supposing to be false, secondly, because ultraviolet stellar radiation calibration belongs to a calibration, due to the impact of camera system point spread function PSF, point target is imaged as a disc of confusion in image planes, the size and target of disc of confusion self is all relevant with PSF to the subtended angle of system, and the total spoke brightness statistics of disc of confusion must introduce error.

Summary of the invention

The technical matters that the present invention solves is: overcome the deficiencies in the prior art, a kind of day blind ultraviolet remote sensing camera Absolute Radiometric Calibration Coefficients modification method is in-orbit proposed, linear regression analysis is carried out in the entrance pupil spoke brightness of experimentally room absolute radiometric calibration equation inverting and the background spoke brightness calculated according to camera imaging pattern and radiation transfer theory model, realizes the correction to terrestrial radiation calibration equation coefficient.

Technical scheme of the present invention is: a kind of day blind ultraviolet-cameras Absolute Radiometric Calibration Coefficients modification method in-orbit, and step is as follows:

(1) Laboratory Radiometric Calibration, obtains absolute radiometric calibration equation and nonuniformity correction coefficient;

11) camera absolute radiometric calibration

Regulate the brightness of camera light source spoke to change from small to big and be followed successively by L ₁, L ₂l _n(L ₁<L ₂< ... <L _n), corresponding camera exports average response and is followed successively by obtain one group of Laboratory Calibration point sequence, adopt least-squares algorithm linear fitting to obtain:

$L=\mathrm{KV}+C(\stackrel{\&OverBar;}{V_1}\&le;V\&le;\stackrel{\&OverBar;}{V_N});$

Wherein K and C is fitting coefficient, and camera is exported average response substitute into above-mentioned equation successively and calculate spoke lightness l value, and calibrate residual error under calculating this camera average response:

${\mathrm{\&epsiv;}}_i=\frac{L-L_i}{L_i}=\frac{k\stackrel{\&OverBar;}{V_i}+c-L_i}{L_i};$

Check whether every bit calibration residual error meets successively | ε _i| <5%, if do not meet, then from scaling point, reject this scaling point, otherwise retain this scaling point, the scaling point retained forms new scaling point sequence, if occur rejecting scaling point in this inspection, then repeats least square linear fit to new scaling point sequence and calibrates residual error with inspection, until this does not occur in checking rejecting scaling point, then the equation that this least-squares algorithm linear fitting obtains is camera absolute radiometric calibration equation:

$L=\mathrm{KV}+C({\stackrel{\&OverBar;}{V}}_{\min }\&le;V\&le;{\stackrel{\&OverBar;}{V}}_{\max });$

Fitting coefficient K and C is camera Absolute Radiometric Calibration Coefficients, represents gain respectively and is biased, for the response of scaling point sequence minimum average B configuration, for the maximum average response of scaling point sequence, for camera linear response range;

12) pixel absolute radiometric calibration

According to camera absolute radiation calibration method, carry out by pixel absolute radiometric calibration to camera, obtaining camera each pixel absolute radiometric calibration equation is:

L＝k _i,jv _i,j+c _i,j；

Wherein v _i,jrepresent the response of pixel (i, j), k _i,jand c _i,jrepresent the gain of pixel (i, j) and be biased;

13) Nonuniformity Correction

Nonuniformity correction coefficient formulas is:

$G_{i,j}=\frac{k_{i,j}}{K}$

$Q_{i,j}=-\frac{C}{K}+G_{i,j}\&CenterDot;\frac{c_{i,j}}{k_{i,j}};$

Wherein G _i,jand Q _i,jfor nonuniformity correction coefficient, i.e. nonuniformity correction gain and nonuniformity correction skew;

(2) obtain camera imaging parameters in-orbit, comprise imaging pattern, imaging time T ₁, orbit elements of satellite (a, e, i, Ω, ω, M ₀) and image in-orbit;

(3) judge camera in-orbit imaging pattern whether be substar imaging, if meet, then enter step (4), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(4) according to imaging time T ₁with orbit elements of satellite (a, e, i, Ω, ω, M ₀) calculate acquisition sub-satellite point geographic latitude

(5) T is judged ₁whether moment satellite is positioned at mid latitudes, and criterion is:

If meet criterion, then enter step (6), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(6) acquisition T is calculated ₁moment sub-satellite point sun altitude h _s

Wherein, δ ₀represent solar declination, φ is expressed as substar latitude, for solar hour angle;

(7) T is judged ₁whether moment satellite meets illumination condition, and criterion is:

h _s>20°；

If meet criterion, then enter step (8), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(8) according to T ₁moment sub-satellite point latitude substar sun altitude h _s, calculate and obtain the brightness of camera entrance pupil spoke

(9) carry out relative nonuniformity correction to image in-orbit, updating formula is:

V _i,j＝G _i,j×v _i,j+Q _i,j；

V _i,jfor the response before image rectification in-orbit, V _i,jfor the response after image rectification in-orbit;

(10) according to camera ground resolution a × b, the full scale region line number N obtaining and can be used for background radiance retrieval is calculated _awith columns N _b:

$N_a=\left[\frac{50}{a}\right]$

$N_b=\left[\frac{50}{b}\right];$

Wherein [] expression rounds; Centered by the pixel of picture centre in-orbit after nonuniformity correction, intercepting size is N _row× N _colrectangular area, N _row, N _colfor positive integer, span is N respectively _row≤ N _aand N _col≤ N _b, calculate to obtain to intercept and calibrate image averaging gray-scale value in region

(11) image averaging gray-scale value is judged whether be positioned at responsing linear range, criterion is:

${\stackrel{\&OverBar;}{V}}_{\min }<V_{\mathrm{orbit}}^T<{\stackrel{\&OverBar;}{V}}_{\max };$

If meet criterion, then according to camera Absolute Radiometric Calibration Coefficients K and C, the brightness of inverting entrance pupil spoke

$L_{\mathrm{calibration}}^T=(V_{\mathrm{orbit}}^T-C)/K;$

Otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(12) the change observation moment is followed successively by T ₁, T ₂... T _m, m be greater than 2 positive integer, calculate camera entrance pupil spoke brightness sequence according to step (3) ~ step (8) the Absolute Radiometric Calibration Coefficients corresponding according to camera and image averaging response according to step (9) ~ step (11) inverting entrance pupil spoke brightness sequence least-squares algorithm linear fitting is adopted to obtain unary linear regression equation COEFFICIENT K _orbitwith C _orbit:

L _orbit＝K _orbitL _calibration+C _orbit；

(13) the unary linear regression equation coefficient utilizing step (12) to try to achieve is revised the camera absolute radiometric calibration equation that step (1) obtains, and obtains revised absolute radiometric calibration equation to be:

L＝K _orbitKV+K _orbitC+C _orbit；

Wherein K _orbitk is gain, K _orbitc+C _orbitbe biased.

The present invention's advantage is compared with prior art:

(1) existing external day blind ultraviolet remote sensing camera based on ultraviolet fixed star single-point in-orbit absolute radiation calibration method there is following defect:

A) one-point method can only determine yield value, if camera response exists amount of bias in whole dynamic range, then one-point method radiation calibration precision cannot ensure;

B) ultraviolet fixed star is point target, due to the impact of camera system point spread function PSF, point target is imaged as a disc of confusion in image planes, the size and target of disc of confusion self is all relevant with PSF to the subtended angle of system, the total spoke brightness of disc of confusion can characterize stellar ultraviolet radiation characteristic, and the statistics of total spoke brightness must introduce error;

The present invention overcomes the above defect of blind ultraviolet remote sensing camera of existing day absolute radiometric calibration in-orbit, proposes blind ultraviolet spectral coverage camera of the general day absolute radiometric calibration equation coefficient modification method in-orbit based on the atmospheric background observation under a kind of constraint condition first;

(2) the present invention is based on day blind ultraviolet spectral coverage the atmospheric background radiation characteristic, adopt the thought of cross-radiometric calibration, meeting under imaging pattern, imaging area, illumination condition observational constraints condition, atmospheric radiation transmission result of calculation can be used as the brightness of real background spoke, the correction of absolute radiometric calibration equation coefficient only depends on laboratory absolute radiometric calibration result and camera the atmospheric background image in-orbit in-orbit, both be easy to the practice and extension of method in engineering, also can meet the requirement of remote sensing camera high frequency time In-flight calibration;

(3) achievement of the present invention can for domestic day blind spectral coverage remote sensor in-orbit absolute radiometric calibration Technical Reference is provided.

Accompanying drawing explanation

The day blind ultraviolet background spoke brightness contrast figure that when Fig. 1 is sun altitude 24 °, LOWTRAN 7 model calculates and S3-4 satellite ultraviolet-cameras is surveyed in-orbit, horizontal ordinate represents wavelength, ordinate represents spectral radiance, in figure, solid line is that model calculates spectral radiance, and dotted line is measured spectra spoke brightness in-orbit;

Fig. 2 is the inventive method process flow diagram.

Embodiment

Day, blind ultraviolet the atmospheric background radiation characteristic analysis was as follows:

1) U.S. CIPS day blind ultraviolet imagery detector in-orbit measured result show: the atmospheric background day, blind UV radiation had the feature of uniform spatial distribution, within the scope of substar 50km × 50km the brightness of the atmospheric background spoke change be less than 5 ‰;

2) theoretical calculation model of day blind ultraviolet spectral coverage the atmospheric background spoke brightness and space-based ultraviolet-cameras are measured comparing result and are shown: day blind ultraviolet band in-orbit the atmospheric background radiation measurement and atmospheric radiation transmission LOWTRAN theoretical calculation model consistance very high, the day blind ultraviolet background spoke brightness contrast figure that when Figure 1 shows that sun altitude 24 °, LOWTRAN 7 model calculates and S3-4 satellite ultraviolet-cameras is surveyed in-orbit, horizontal ordinate represents wavelength, ordinate represents spectral radiance, wherein solid line is model calculation value, and dotted line is measured value in-orbit.Coherence request ultraviolet-cameras inflight measurement meets following three observation conditions:

I. detector observed pattern is substar imaging;

Ii. substar sun altitude is greater than 20 degree;

Iii. substar regional geography latitude is mid latitudes;

3) utilize LOWTRAN simulation calculation day blind ultraviolet spectral coverage the atmospheric background spoke brightness results to show: the brightness of substar the atmospheric background spoke is only relevant with solar zenith angle, substar season, geographic position, have nothing to do with other atmospheric conditions such as clutter reflections rate, visibility, sexual intercourse condition.

Based on above analysis result, a kind of day blind ultraviolet remote sensing camera Absolute Radiometric Calibration Coefficients modification method is in-orbit proposed: under the constraint of certain camera observation condition, radiation transmitting software is calculated the atmospheric background radiation as true measurement in-orbit, linear regression analysis is carried out with the spoke brightness value of experimentally room calibration equation inverting, revise laboratory absolute radiometric calibration equation coefficient, as shown in Figure 1:

(1) Laboratory Radiometric Calibration, obtains absolute radiometric calibration equation and nonuniformity correction coefficient;

11) absolute radiometric calibration

Camera running parameter is set, regulates the brightness of camera light source spoke to change from small to big and be followed successively by L ₁, L ₂l _n(L ₁<L ₂< ... <L _n), corresponding camera exports average response and is followed successively by obtain one group of Laboratory Calibration point sequence, adopt least-squares algorithm linear fitting to obtain:

$L=\mathrm{KV}+C(\stackrel{\&OverBar;}{V_1}\&le;V\&le;\stackrel{\&OverBar;}{V_N});$

Wherein K and C is fitting coefficient, and camera is exported average response substitute into above equation successively and calculate spoke lightness l value, and calibrate residual error under calculating this camera average response:

${\mathrm{\&epsiv;}}_i=\frac{L-L_i}{L_i}=\frac{k\stackrel{\&OverBar;}{V_i}+c-L_i}{L_i};$

Considering camera low side and high-end non-linear response characteristic, in order to ensure Laboratory Radiometric Calibration precision, taking following methods to carry out the rejecting of nonlinear calibration point, the corresponding spoke brightness of scaling point of rejecting can carry out radiation calibration process under other camera running parameters.

Check whether every bit calibration residual error meets successively | ε _i| <5%, if do not meet, then from scaling point, reject this scaling point, otherwise retain this scaling point, the scaling point retained forms new scaling point sequence, if occur rejecting scaling point in this inspection, then repeats least square linear fit to new scaling point sequence and calibrates residual error with inspection, otherwise the equation that this least-squares algorithm linear fitting obtains is camera absolute radiometric calibration equation:

$L=\mathrm{KV}+C({\stackrel{\&OverBar;}{V}}_{\min }\&le;V\&le;{\stackrel{\&OverBar;}{V}}_{\max });$

Fitting coefficient K and C is camera Absolute Radiometric Calibration Coefficients, represents gain respectively and is biased, for the response of scaling point sequence minimum average B configuration, for the maximum average response of scaling point sequence, for camera linear response range;

12) pixel absolute radiometric calibration

According to camera absolute radiation calibration method, carry out by pixel absolute radiometric calibration to camera, obtaining camera each pixel absolute radiometric calibration equation is:

L＝k _i,jv _i,j+c _i,j；

Wherein v _i,jrepresent the response of pixel (i, j), k _i,jand c _i,jrepresent the gain of pixel (i, j) and be biased;

13) Nonuniformity Correction

Nonuniformity correction coefficient formulas is:

$G_{i,j}=\frac{k_{i,j}}{K}$

$Q_{i,j}=-\frac{C}{K}+G_{i,j}\&CenterDot;\frac{c_{i,j}}{k_{i,j}};$

Wherein G _i,jand Q _i,jfor nonuniformity correction coefficient, i.e. nonuniformity correction gain and nonuniformity correction skew;

(2) obtain camera imaging parameters in-orbit, comprise imaging pattern, imaging time T ₁, orbit elements of satellite (a, e, i, Ω, ω, M ₀) and image in-orbit;

(3) judge camera in-orbit imaging pattern whether be substar imaging, if meet, then enter step (4), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(4) according to imaging time T and orbit elements of satellite (a, e, i, Ω, ω, M ₀) calculate sub-satellite point geographic latitude

41) T moment eccentric anomaly E is calculated

Use iterative method Kepler's equation

E _i+1＝M+e sin E _i；

Wherein, e is excentricity, and M is mean anomaly; When | E _i+1-E _i| < ε, gets E=E _i+1; ε is given accuracy, and the initial value of iteration gets E ₁=M;

42) T moment true anomaly f is calculated

$\tan \frac{f}{2}=\sqrt{\frac{1+e}{1-e}}\tan \frac{E}{2};$

Wherein with at same quadrant;

43) T moment the earth's core is calculated apart from r

$r=\frac{a(1-e^2)}{1+e\cos f};$

Wherein a is semi-major axis;

44) T moment latitude argument u is calculated

u＝ω+f；

Wherein ω is argument of perigee;

45) the position x of T moment satellite in celestial coordinate system is calculated, y, z

x＝r(cosΩcos u-sinΩsin u cos i)

y＝r(sinΩcos u+cosΩsin u cos i)

z＝r sin u sin i；

Wherein Ω is right ascension of ascending node;

46) T moment sub-satellite point longitude and latitude α is calculated, φ

$\sin \mathrm{\&phi;}=\frac{Z}{r}$

47) T moment sub-satellite point geographic latitude is calculated

(5) T is judged ₁whether moment satellite is positioned at mid latitudes, and criterion is:

If meet criterion, then enter step (6), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(6) T is calculated ₁moment sub-satellite point sun altitude h _s

Wherein, δ ₀represent solar declination, φ is expressed as substar latitude, for solar hour angle;

(7) T is judged ₁whether moment satellite meets illumination condition, and criterion is:

h _s>20°；

If meet criterion, then enter step (8), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(8) according to T ₁moment sub-satellite point latitude substar sun altitude h _s, calculate the brightness of camera entrance pupil spoke

(9) carry out relative nonuniformity correction to image in-orbit, updating formula is:

V _i,j＝G _i,j×v _i,j+Q _i,j；

V _i,jfor the response before image rectification in-orbit, V _i,jfor the response after image rectification in-orbit;

(10) according to camera ground resolution a × b, ground resolution unit is km, calculates the calibration region line number N that can be used at most background radiance retrieval _awith columns N _b:

$N_a=\left[\frac{50}{a}\right]$

$N_b=\left[\frac{50}{b}\right];$

Wherein [] expression rounds; Size is intercepted for N centered by the pixel of picture centre in-orbit after nonuniformity correction _row× N _colrectangular area, N _row, N _colfor positive integer, span is N respectively _row≤ N _aand N _col≤ N _b, calculate and intercept image averaging gray-scale value in calibration region

(11) image averaging gray-scale value is judged whether be positioned at responsing linear range, criterion is:

${\stackrel{\&OverBar;}{V}}_{\min }<V_{\mathrm{orbit}}^T<{\stackrel{\&OverBar;}{V}}_{\max };$

If meet criterion, then according to camera Absolute Radiometric Calibration Coefficients K and C, the brightness of inverting entrance pupil spoke

$V_{\mathrm{calibration}}^T=(V_{\mathrm{orbit}}^T-C)/K;$

Otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(12) the change observation moment is followed successively by T ₁, T ₂... T _m, m be greater than 2 positive integer, calculate camera entrance pupil spoke brightness sequence according to step (3) ~ step (8) the Absolute Radiometric Calibration Coefficients corresponding according to camera and image averaging response according to step (9) ~ step (11) Inversion Calculation camera entrance pupil spoke brightness sequence least-squares algorithm linear fitting is adopted to obtain unary linear regression equation COEFFICIENT K _orbitwith C _orbit:

L _orbit＝K _orbitL _calibration+C _orbit；

(13) the unary linear regression equation coefficient utilizing step (12) to try to achieve is revised the camera absolute radiometric calibration equation that step (1) obtains, and obtains revised absolute radiometric calibration equation to be:

L＝K _orbitKV+K _orbitC+C _orbit；

Wherein K _orbitk is gain, K _orbitc+C _orbitbe biased.

The content be not described in detail in instructions of the present invention belongs to ability in the known technology of technician.

Claims (1)

1. a day blind ultraviolet-cameras Absolute Radiometric Calibration Coefficients modification method in-orbit, is characterized in that step is as follows:

(1) Laboratory Radiometric Calibration, obtains absolute radiometric calibration equation and nonuniformity correction coefficient;

11) camera absolute radiometric calibration

Regulate the brightness of camera light source spoke to change from small to big and be followed successively by L ₁, L ₂l _n(L ₁<L ₂< ... <L _n), corresponding camera exports average response and is followed successively by obtain one group of Laboratory Calibration point sequence, adopt least-squares algorithm linear fitting to obtain:

$L=\mathrm{KV}+C({\stackrel{\&OverBar;}{V}}_1\&le;V\&le;{\stackrel{\&OverBar;}{V}}_N);$

Wherein K and C is fitting coefficient, and camera is exported average response substitute into above-mentioned equation successively and calculate spoke lightness l value, and calibrate residual error under calculating this camera average response:

${\mathrm{\&epsiv;}}_i=\frac{L-L_i}{L_i}=\frac{k{\stackrel{\&OverBar;}{V}}_i+c-L_i}{L_i};$

Check whether every bit calibration residual error meets successively | ε _i| <5%, if do not meet, then from scaling point, reject this scaling point, otherwise retain this scaling point, the scaling point retained forms new scaling point sequence, if occur rejecting scaling point in this inspection, then repeats least square linear fit to new scaling point sequence and calibrates residual error with inspection, until this does not occur in checking rejecting scaling point, then the equation that this least-squares algorithm linear fitting obtains is camera absolute radiometric calibration equation:

$L=\mathrm{KV}+C({\stackrel{\&OverBar;}{V}}_{\min }\&le;V\&le;{\stackrel{\&OverBar;}{V}}_{\max });$

Fitting coefficient K and C is camera Absolute Radiometric Calibration Coefficients, represents gain respectively and is biased, for the response of scaling point sequence minimum average B configuration, for the maximum average response of scaling point sequence, for camera linear response range;

12) pixel absolute radiometric calibration

According to camera absolute radiation calibration method, carry out by pixel absolute radiometric calibration to camera, obtaining camera each pixel absolute radiometric calibration equation is:

L＝k _i,jv _i,j+c _i,j；

Wherein v _i,jrepresent the response of pixel (i, j), k _i,jand c _i,jrepresent the gain of pixel (i, j) and be biased;

13) Nonuniformity Correction

Nonuniformity correction coefficient formulas is:

$G_{i,j}=\frac{k_{i,j}}{K}$

$Q_{i,j}=-\frac{C}{K}+G_{i,j}\&CenterDot;\frac{c_{i,j}}{k_{i,j}};$

Wherein G _i,jand Q _i,jfor nonuniformity correction coefficient, i.e. nonuniformity correction gain and nonuniformity correction skew;

(2) obtain camera imaging parameters in-orbit, comprise imaging pattern, imaging time T ₁, orbit elements of satellite (a, e, i, Ω, ω, M ₀) and image in-orbit;

(3) judge camera in-orbit imaging pattern whether be substar imaging, if meet, then enter step (4), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(4) according to imaging time T ₁with orbit elements of satellite (a, e, i, Ω, ω, M ₀) calculate acquisition sub-satellite point geographic latitude

(5) T is judged ₁whether moment satellite is positioned at mid latitudes, and criterion is:

If meet criterion, then enter step (6), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(6) acquisition T is calculated ₁moment sub-satellite point sun altitude h _s

Wherein, δ ₀represent solar declination, φ is expressed as substar latitude, for solar hour angle;

(7) T is judged ₁whether moment satellite meets illumination condition, and criterion is:

h _s>20°；

If meet criterion, then enter step (8), otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(8) according to T ₁moment sub-satellite point latitude substar sun altitude h _s, calculate and obtain the brightness of camera entrance pupil spoke

(9) carry out relative nonuniformity correction to image in-orbit, updating formula is:

V _i,j＝G _i,j×v _i,j+Q _i,j；

V _i,jfor the response before image rectification in-orbit, V _i,jfor the response after image rectification in-orbit;

(10) according to camera ground resolution a × b, the full scale region line number N obtaining and can be used for background radiance retrieval is calculated _awith columns N _b:

$\begin{array}{c}{N}_a=\left[\frac{50}{a}\right]\\ N_b=\left[\frac{50}{b}\right]\end{array};$

Wherein [] expression rounds; Centered by the pixel of picture centre in-orbit after nonuniformity correction, intercepting size is N _row× N _colrectangular area, N _row, N _colfor positive integer, span is N respectively _row≤ N _aand N _col≤ N _b, calculate to obtain to intercept and calibrate image averaging gray-scale value in region

(11) image averaging gray-scale value is judged whether be positioned at responsing linear range, criterion is:

${\stackrel{\&OverBar;}{V}}_{\min }<V_{\mathrm{orbit}}^T<{\stackrel{\&OverBar;}{V}}_{\max };$

If meet criterion, then according to camera Absolute Radiometric Calibration Coefficients K and C, the brightness of inverting entrance pupil spoke $L_{\mathrm{calibration}}^T:$

$L_{\mathrm{calibration}}^T=(V_{\mathrm{orbit}}^T-C)/K;$

Otherwise rebound step (2) obtains new camera imaging parameters in-orbit again;

(12) the change observation moment is followed successively by T ₁, T ₂... T _m, m be greater than 2 positive integer, calculate camera entrance pupil spoke brightness sequence according to step (3) ~ step (8) the Absolute Radiometric Calibration Coefficients corresponding according to camera and image averaging response according to step (9) ~ step (11) inverting entrance pupil spoke brightness sequence least-squares algorithm linear fitting is adopted to obtain unary linear regression equation COEFFICIENT K _orbitwith C _orbit:

L _orbit＝K _orbitL _calibration+C _orbit；

(13) the unary linear regression equation coefficient utilizing step (12) to try to achieve is revised the camera absolute radiometric calibration equation that step (1) obtains, and obtains revised absolute radiometric calibration equation to be:

L＝K _orbitKV+K _orbitC+C _orbit；

Wherein K _orbitk is gain, K _orbitc+C _orbitbe biased.